Rules:
1. The machine must be stationary.
2. The machine must operate without human aid – only the pushbutton and potentiometer may be touched in order to launch the ball.
3. The machine should be able to re-load and launch a second ball without the need of human aid other than touching the pushbutton or potentiometer.

Here is one of the catapult kits (the potentiometers have not arrived yet):

The Arduino catapult competition was held on Friday, November 16. There were four working catapults, but all four violated the rules in some way.